Cholinergic amacrine cells of the rabbit retina contain glutamate decarboxylase and gamma-aminobutyrate immunoreactivity.

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RESUMO

The transmitters acetylcholine and gamma-aminobutyrate (GABA) play critical roles in the formation of receptive-field properties of retinal ganglion cells. In rabbit retina, cholinergic amacrine and displaced amacrine cells were identified by immunohistochemical staining for the enzyme choline acetyltransferase and by their avid accumulation of the fluorescent dye 4',6-diamidino-2-phenylindole. Several GABA-immunoreactive and glutamate decarboxylase-immunoreactive cell types, including a prominent population of small, round amacrine and displaced amacrine cells, were also identified. Double-label experiments demonstrated that all amacrine and displaced amacrine cells that prominently accumulate 4',6-diamidino-2-phenylindole contain GABA and glutamate decarboxylase immunoreactivity. However, not all GABA-immunoreactive cells accumulate this dye. Quantitative analysis of the ganglion cell layer of whole mount preparations of the retina showed that choline acetyltransferase-immunoreactive cells and the majority of GABA-immunoreactive cells have a small, round shape and similar cell density profiles that parallel that of displaced amacrine cells. These studies establish that cholinergic cells are a major subpopulation of GABA-immunoreactive amacrine and displaced amacrine cells. The role these cells have in the formation of ganglion cell receptive-field properties may be parsimoniously explained by an excitatory postsynaptic action mediated by acetylcholine and an inhibitory presynaptic action mediated by GABA.

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